Okay, so there are now three of them.
I have a fairly tentative approach to social applications. I'm not on Facebook, and my Twitter account remains untweeted. But I thought I'd give foursquare a go, and I've been on it for a few weeks now, dutifully checking in whenever I remember, so that my two friends (who incidentally live miles from York) will know where I am (usually a long way away). Not very useful yet, though I can see how it could be if I could just reach that critical mass of friends. It's not helped that so few of my non-virtual friends have smartphones.
However, the price of smartphones will continue to drop, and in no great time they will presumably be the norm. Meanwhile I look forward to the time when I can't count all my foursquare friends on the fingers of one hand. Maybe when that happens foursquare will give me a badge?